Functional Programming¶
Major libraries supporting functional programming in JavaScript
We will be primarily using Ramda for our examples below.
Importing the library:
R = require('ramda');
Empty¶
Checking whether something is empty (an object or an array or a string):
> R.isEmpty({})
true
> R.isEmpty([])
true
> R.isEmpty('')
true
This function will appropriately return false in other cases:
> R.isEmpty(0)
false
> R.isEmpty(1)
false
> R.isEmpty(true)
false
> R.isEmpty(false)
false
> R.isEmpty(null)
false
> R.isEmpty(undefined)
false
> R.isEmpty(NaN)
false
> R.isEmpty({1: 2})
false
> R.isEmpty([1])
false
> R.isEmpty('a')
false
Search¶
Searching for the index of an object in a array:
> R.findIndex(x => x == 2, [1, 2, 3])
1
The index is 0 based. The first argument is a predicate
which returns true when a suitable search criterion is
satisfied. Here, we are looking for the first element in the
array whose value is 2. Hence the criterion is x == 2.
The predicate function is written as an arrow function x => x ==2.
When no element of the array satisfies the given predicate, it returns -1:
> R.findIndex(x => x == 2, [1, 4, 3])
-1
The index of the first match is returned always:
> R.findIndex(x => x == 2, [1, 2, 2, 3])
1
Searching in an array of objects based on the value of an attribute:
> R.findIndex(x => x.v == 2, [{v : 4}, {v : 3}, {v: 2}])
2
Finding the array element:
> R.find(x => x == 2, [1, 2, 3])
2
> R.find(x => x == 2, [1, 4, 3])
undefined
> R.find(x => x == 2, [1, 2, 2, 3])
2
> R.find(x => x.v == 2, [{v : 4}, {v : 3}, {v: 2}])
{ v: 2 }
If there is no array element satisfying the criterion in the predicate,
then undefined is returned.